The redesigned 2013 Mercedes-Benz SL-Class hard­top road­ster is cur­rently the industry’s most dif­fi­cult vehi­cle to obtain, accord­ing to a report from TrueCar.com and a slideshow from Forbes. Sub­com­pact cars are in short sup­ply on deal­ers’ lots. BMW deal­ers have the hardest-to-get model lines at an aver­age 24 days’ sup­ply, with Hyundai at 25 days, Mini at 26 days, Kia at 29 days and Audi at 30 days.